A variety of approaches to stratum disposal of radioactive wastes have been heretofore proposed. For instance, stratum disposal of high-level radioactive wastes has been projected with a system, which conducts stabilizing treatment of the wastes into vitrified wastes by melting the wastes together with a glass material at high temperatures to pour into a stainless steel canister, and stores the vitrified wastes tightly in a thick steel-plate airtight container called an over-pack to effect stratum disposal of the over-pack through a buffer member into a rock bed at a depth in the range of several hundred to several ten hundred meters from the ground.
In the above stratum disposal system, there are basically four patterns of layouts adaptable to underground stationary disposal of over-packs as shown in FIGS. 46 to 49. FIG. 46 shows the layout of a horizontal disposal-gallery pattern, in which a pair of left and right main galleries (conveyance galleries) 1, 1 have therebetween horizontally or vertically inclined disposal galleries (disposal spaces) 2. The disposal galleries 2 are obtained by boring in parallel, at given intervals, to ensure that underground stationary disposal of over-packs A is attainable sidewise within each disposal gallery 2 at given intervals in a longitudinal direction of the galleries. FIG. 47 shows the layout of a vertical disposal, vertical shaft pattern, in which an upper main gallery (conveyance gallery) 1 and a lower gallery 1′ have therebetween vertical disposal holes (disposal vertical shafts: disposal spaces) 3. The disposal spaces 3 are obtained by boring in parallel at given intervals to ensure that underground stationary disposal of over-packs A is attainable lengthwise within each disposal vertical shaft 3, at given intervals, in a vertical direction of the galleries.
FIG. 48 shows the layout of a horizontal disposal, hole pattern, in which a disposal gallery (conveyance gallery) 4 has at the opposite walls thereof horizontal disposal holes (disposal spaces) 5. The disposal spaces 5 are obtained by boring at given intervals in a longitudinal direction of the gallery to ensure that underground stationary disposal of over-packs A is attainable sidewise within each disposal hole 5. FIG. 49 shows the layout of a vertical disposal-hole pattern, in which the disposal gallery 4 has at the bottom thereof vertical disposal holes (disposal spaces) 6. The disposal spaces 6 are obtained by boring at given intervals in the longitudinal direction of the gallery to ensure that underground stationary disposal of over-packs A is attainable lengthwise within each disposal hole 6.
The above stratum disposal system needs monitoring of the displacement of rock beds, the permeation of underground water and the like at the demonstration stage before operations or at the actual operational stage. In a prototype disposal field in Sweden, a demonstration has been conducted to ascertain a barrier performance, as shown in FIG. 50.
In the above demonstration, monitoring of the swelling behavior of buffer members C firstly takes place under the condition that an upper space 4 is refilled after pseudo canisters A and the buffer members C have been fixed in full-sized disposal holes 6, as shown in FIGS. 50 and 51. A large number of sensors 101 are embedded to check the behavior of the buffer members. In addition, about 30 pieces of drilled holes 103 obtained by drilling from measurement galleries 102 adjoining to each other to a prototype disposal field 100 (gallery 4 above the disposal holes) have therein communication cables to obtain data sent from the sensors.
However, the above conventional monitoring method has the disadvantages of requiring a large number of sensors, drilled holes and communication cables, and taking much time for installation works and maintenance, resulting in an increase in cost. Or, in certain circumstances, maintenance is not executable, so that the above conventional monitoring method fails to keep up with monitoring.
In addition, the monitoring equipment such as the sensors and the communication cables applied in a stratum disposal field needs to be good for a long-term service under the high-temperature/high-pressure environment. Thus, monitoring equipment having durability is required. However, as described in a later instance, the durability of the monitoring equipment is considered to be not so sufficient for the long-term service, so that the conventional monitoring method has the disadvantage of finding difficulty in exchanging once-embedded sensors and cables with new ones.
As to the durability of the sensors, a demonstration has been conducted to ascertain the performance of bentonite plugs and concrete plugs in a gallery existing at a depth of 420 meters from the ground in Canada. In this demonstration, 800 pieces or more of sensors were installed to check the performance of the bentonite plugs, with the result that an operating ratio of the sensors has dropped to the level of 80% in three years. In addition, it is reported that the computerized execution of typical civil engineering works frequently causes some failures in about 30% of the sum total of sensors until the works covering a period of several years are completed.
The present invention has been undertaken in view of the problems with the above conventional monitoring method. A first object of the present invention is to provide a gallery monitoring method, wherein in monitoring as in a stratum disposal field and the like for wastes, a reduction of the number of sensors, drilled holes and communication cables is attainable, and the exchange or maintenance of the sensors, the communication cables and the like is facilitated.
A second object of the present invention is to provide a gallery monitoring method, wherein in monitoring as in a stratum disposal field and the like for wastes, a reduction of the number of drilled holes and communication cables is attainable, an artificial barrier is prevented from having any water passage, and a monitoring device configured as a small-sized inexpensive device is available.
In the stratum disposal field as shown in FIGS. 46 to 49, upon completion of the works of underground stationary disposal of the over-packs A, not only an access gallery (such as a vertical shaft, an inclined shaft, a spiral gallery) between the ground facilities and the underground disposal field but also the main gallery, the connecting gallery and the like in the underground disposal field are refilled, resulting in the closure of the disposal field (not shown).
A basic technical concept prevailing at present in the above stratum disposal system is that care for the disposal field is not necessary after the disposal field has been closed, specifically, all the galleries and the like have been refilled. From a social point of view or a standpoint of a need to give regional residents a sense of security, it is, however, believed that there is a need to monitor the over-packs and their surroundings for a long period of time after closure of the disposal field occurs.
The above need is believed to be realizable typically with a monitoring system, which uses a sensor 200 embedded around the over-packs A within the disposal gallery 2, and further uses a communication cable (such as a wire and an optical fiber) 201, as shown in FIG. 52. This arrangement establishes connection between the sensor 200 and the ground facilities to ensure that monitoring is executable through the communication cable 201. In this case, the communication cable 201 is to be laid underground in the range of the disposal gallery 2 to the inside of the access gallery such as the vertical shaft 7. It is noted that sensor power is also fed from the ground facilities through the cable.
However, the above conventional communication cable system has the following problems.                (1) It is feared that the cable having been laid underground within the access gallery leads to the water passage, and further to the selective migration route of nuclides in future.        (2) The underground cable existing under the underground high-temperature/high-pressure environment is limited in durability, and also covers the range of a long distance, so that degradation, disconnection and the like of the cable result in long-term monitoring of difficulty.        (3) The underground sensor existing under the underground high-temperature/high-pressure environment is limited in durability, resulting in long-term monitoring of difficulty as well.        
As one of the approaches to solving the problems with the above communication cable system, a monitoring device and a ground information transmitting device in a disposal field for radioactive wastes have been disclosed in Japanese Patent Laid-open No. 7-306299. Referring to FIG. 53, the patent disclosure relates to a monitoring system in a disposal field for underground stationary disposal of radioactive wastes 301 within a cavity 300 constructed in the ground. Ground information is detected with a group of sensors 302 comprised of sensors 302a1 through 302an embedded in the ground in the vicinity of the cavity 300. A measured data signal sent from each sensor 302a is transmitted as elastic waves (such as electric distorted vibrations generated by an electric distortion element sound source) EV through an antenna 304 of a transmitter/receiver 303 to ensure that the elastic waves EV having made propagation through the ground are received with a ground or underground measuring device 305. The transmitter/receiver 303 is operated with power generated by a thermo-electric conversion element 306 operated by taking advantage of heat emitted from the wastes.
However, the above monitoring system with the elastic waves has the following problems. (1) It is difficult to propagate the elastic waves from the deep underground part at a depth in the range of several hundred to several tens of hundred meters from the ground without causing attenuation. In addition, a large-sized large-capacity transmission/receiver is required for the transmitter/receiver 303 to propagate the elastic waves toward the ground facilities. (2) It is difficult to cover the power for the group 302 of sensors and the transmitter/receiver 303 only with the heat emitted from the radioactive wastes. (3) Each sensor 302a is existent in the high-temperature/high-pressure underground part, resulting in long-term monitoring of difficulty.
The present invention has been undertaken in view of the problems of the above conventional monitoring systems associated with the communication cable system and with elastic waves. Accordingly, a third object of the present invention is to provide a monitoring system for stratum disposal wastes which lessens or eliminates the conventional disadvantage of allowing the communication cable to lead to the water passage and further to the migration route for future contamination. The monitoring of the behavior of the wastes and their surroundings is executable securely over a long period of time.